Constraints on μ-distortion fluctuations and primordial non-Gaussianity from Planck data

Abstract

We use the Planck HFI channel maps to make an all sky map of μ-distortion fluctuations. Our μ-type distortion map is dominated by the y-type distortion contamination from the hot gas in the low redshift Universe and we can thus only place upper limits on the μ-type distortion fluctuations. For the amplitude of μ-type distortions on 10′ scales we get the limit on root mean square (rms) value μrms10′< 6.4× 10−6, a limit 14 times stronger than the COBE-FIRAS (95% confidence) limit on the mean of ⟨ μ ⟩<90× 10−6. Using our maps we also place strong upper limits on the auto angular power spectrum of μ, Cℓμμ and the cross angular power spectrum of μ with the CMB temperature anisotropies, Cℓμ T. The strongest observational limits are on the largest scales, ℓ(ℓ+1)/(2π)Cℓμμ|ℓ=2−26<(2.3± 1.0)× 10−12 and ℓ(ℓ+1)/(2π)Cℓμ T|ℓ=2−26<(2.6± 2.6)× 10−12 K. Our observational limits can be used to constrain new physics which can create spatially varying energy release in the early Universe between redshifts 5× 104≲ z≲ 2× 106. We specifically apply our observational results to constrain the primordial non-Gaussianity of the local type, when the source of μ-distortion is Silk damping, for very squeezed configurations with the wavenumber for the short wavelength mode 46 ≲ kS ≲ 104 Mpc−1 and for the long wavelength mode kL≈ 10−3 Mpc−1. Our limits on the primordial non-Gaussianity parameters are fNL<105, τNL<1.4× 1011 for kS/kL≈ 5× 104− 107. We also give a new derivation of the evolution of the μ-distortion fluctuations through the y-distortion era and the recombination epoch until today resulting in very simple expressions for the cross and auto power spectra in the squeezed limit. We also introduce mixing of Bose-Einstein spectra due to Silk damping and yBE-type distortions. The μ-type distortion map and masks are now publicly available.